Methods of treating subterranean formations using solid particles and other larger solid materials

ABSTRACT

Improved methods of treating subterranean formations using solid particles and other larger solid materials are provided. The methods are basically comprised of the steps of introducing a carrier fluid containing suspended solid particles which have been coated with a non-hardening tackifying agent into a subterranean formation, mixing a solid material of larger size with the tackifying compound coated solid particles whereby the solid particles stick to the larger solid material and the solid particles and larger solid material are uniformly suspended in the carrier fluid and depositing the larger solid material and the tackifying compound coated smaller solid particles in the subterranean formation.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of application Ser. No.10/235,353 filed on Sep. 5, 2002

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to improved methods of treatingsubterranean formations using solid particles and other larger solidmaterials.

[0004] 2. Description of the Prior Art

[0005] Hydrocarbon producing subterranean formations penetrated by wellbores are often treated by forming gravel packs of solid particlesadjacent to the subterranean formation and/or fracturing thesubterranean formation and depositing proppant particle packs in thefractures.

[0006] In gravel packing operations, solid particles, referred to in theart as gravel, are suspended in water or a viscous fluid at the surfaceand carried to the well bore in which the gravel pack is to be placed ata designed gravel concentration and pump rate. As the gravel is beingplaced in the well bore, the carrier fluid is either returned to thesurface via the washpipe or leaked off into the formation. The gravelpack produced functions as a filter to separate formation sand and solidfines from produced fluids while permitting the produced fluids to flowinto and through the well bore.

[0007] Another subterranean formation treatment is hydraulic fracturing.That is, a viscous treating fluid, referred to in the art as afracturing fluid, is pumped through the well bore into a subterraneanformation or zone to be stimulated at a rate and pressure such thatfractures are formed and extended into the subterranean formation. Theviscous fracturing fluid includes proppant particles, e.g., graded sand,suspended therein which are carried into the fractures. The proppantparticles are deposited in the fractures when the viscous fracturingfluid is broken (the viscosity is reduced) and recovered. The proppantparticles function to prevent the formed fractures from closing and theclosing pressure of the fractures forms the proppant particles intopacks. The proppant particle packs maintain the fractures open and formconductive channels through which produced fluids can flow to the wellbore.

[0008] A problem often experienced in the use of gravel packs andpropped fractures is that as formation fluids are produced, the gravelor proppant particles flow-back with the formation fluids. In additionto losing the conductivity of the fractures, the flow-back of theproppant particles with formation fluids is very detrimental in that theresulting solids in the produced formation fluids erode metal goods,plug piping and vessels and cause damage to valves, instruments andother production equipment.

[0009] In order to prevent gravel or proppant particle flow-back, otherlarger solid materials have been combined with the smaller particles inattempts to prevent flow-back. However, a problem encountered with theuse of larger solid material with the smaller gravel or proppantparticles is that the larger solid material segregates from the smallerparticles by floating to the top or settling to the bottom of thecarrying fluid. This in turn results in uneven distribution of thesmaller particles and larger solid materials which results in theflow-back of both the smaller particles and the larger solid materialswith the produced fluids.

[0010] Thus, there are needs for improved methods of treatingsubterranean formations utilizing small solid particles and larger solidmaterials whereby flow-back of the particles and materials does notoccur.

SUMMARY OF THE INVENTION

[0011] The present invention provides improved methods of treatingsubterranean formations using solid particles and other larger solidmaterials which meet the needs described above and overcome thedeficiencies of the prior art. A method of this invention is basicallycomprised of the following steps. A carrier fluid containing suspendedsolid particles which have been coated with a non-hardening tackifyingcompound is introduced into the subterranean formation. A particulate orother shaped solid material of larger size than the solid particles ismixed with the tackifying compound coated smaller solid particlessuspended in the carrier fluid whereby the smaller solid particles stickto the larger solid material and the larger solid material is suspendedin the carrier fluid along with the smaller solid particles. Thereafter,the larger solid material and the tackifying compound coated smallersolid particles stuck thereto are deposited in the subterraneanformation so that upon flowing back fluid from the formation the smallersolid particles and the larger solid material do not flow-back.

[0012] The smaller solid particles which are coated with thenon-hardening tackifying compound are selected from the group of gradedsand, walnut hulls, bauxite, ceramic materials, glass materials andpolymer beads. The larger solid material is selected from the groupconsisting of fibers, shavings, platelets, deformable particles andirregular shaped particulate or pieces.

[0013] Another method of this invention for treating a subterraneanformation is comprised of the following steps. A viscous fracturingfluid containing suspended solid particles which have been coated with anon-hardening tackifying compound is introduced into fractures formed inthe subterranean formation. Deformable particles of a larger size thanthe proppant particles are mixed with the tackifying compound coatedproppant particles suspended in the fracturing fluid whereby the smallerproppant particles stick to the larger deformable particles and thedeformable particles are uniformly suspended in the fracturing fluidalong with the proppant particles. The deformable particles and thesmaller tackifying compound coated proppant particles stuck thereto aredeposited in the fractures in the subterranean formation so that uponflowing back fluid from the formation the proppant particles and thedeformable particles do not flow-back.

[0014] The objects, features and advantages of the present inventionwill be readily apparent to those skilled in the art upon a reading ofthe description of preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0015] By the present invention, improved methods of treatingsubterranean formations using solid particles and other larger solidmaterials are provided. A method of the invention basically comprisesthe following steps. A carrier fluid containing suspended solidparticles which have been coated with a non-hardening tackifyingcompound is introduced into a subterranean formation. A particulate orother shaped solid material of larger size than the solid particles aremixed with the tackifying compound coated solid particles suspended inthe carrier fluid whereby the smaller solid particles stick to thelarger solid material and the larger solid material is uniformlysuspended in the carrier fluid along with the solid particles.Thereafter, the larger solid material and the tackifying compound coatedsolid particles stuck thereto are deposited in the subterraneanformation so that upon flowing back fluid from the formation the solidparticles and the larger solid material do not flow-back.

[0016] The carrier fluid utilized in accordance with this invention ispreferably selected from the group consisting of an aqueous gelledliquid, an emulsion, a foamed fluid, a viscoelastic surfactant fluid andwater. Of these, an aqueous gelled liquid is preferred. The waterutilized in the aqueous gelled liquid can be fresh water or salt water.The term “salt water” is used herein to mean unsaturated salt solutionsand saturated salt solutions including brines and seawater. A variety ofgelling agents can be included in the carrier fluid to increase theviscosity thereof and suspend the solid particles and larger solidmaterial therein. The gelling agents can be natural and derivatizedpolysaccharides which are soluble, dispersible or swellable in anaqueous liquid to yield viscosity to the liquid. One group, for example,of polysaccharides which are suitable for use in accordance with thepresent invention includes galactomannan gums such as guar gum and thelike. Modified gums such as carboxyalkyl and hydroxyalkyl derivativeslike carboxymethyl guar and hydroxypropyl guar can also be employed.Doubly derivatized gums such as carboxymethylhydroxypropyl guar can alsobe used. Modified celluloses and derivatives thereof can also beemployed. Examples of water-soluble cellulose ethers which can be usedinclude, but are not limited to, carboxyethylcellulose,carboxymethylcellulose, carboxymethylhydroxyethylcellulose,hydroxyethylcellulose, hydroxypropylcellulose and the like. The gellingagent is included in the aqueous carrier fluid in an amount in the rangeof from about 0.01% to about 3% by weight of the carrier fluid.

[0017] In order to further enhance the development of the viscosity ofthe carrier fluid, the gelling agent used can be cross-linked by theaddition of a cross-linking agent to the aqueous carrier fluid. Thecross-linking agent can comprise a borate releasing compound or any ofthe well known transition metal ions which are capable of creating across-linked structure with the particular gelling agent utilized.Preferred cross-linking agents for use with the above described gellingagents include, but are not limited to, borate releasing compounds, asource of titanium ions, a source of zirconium ions, a source ofantimony ions and a source of aluminum ions. When used, a cross-linkingagent of the above types is included in the aqueous treating fluid in anamount in the range of from above 0.01% to about 1% by weight of thegelling agent therein.

[0018] The solid particles suspended in the carrier fluid can include,but are not limited to, graded sand, walnut hulls, bauxite, ceramicmaterials, glass materials and polymer beads. Of these, graded sand ispreferred. The solid particles are generally included in the carrierfluid in an amount in the range of from about 0.1 pounds per gallon toabout 34 pounds per gallon.

[0019] The non-hardening tackifying compound utilized in accordance withthis invention can be a liquid or a solution of a compound capable offorming a non-hardening tacky coating on the proppant particlessuspended in the carrier fluid.

[0020] A preferred group of tackifying compounds which can be utilizedin accordance with this invention are polyamides which are liquids orinsolvent solutions at the temperature of the subterranean formation tobe treated such that the polyamides are, by themselves, non-hardeningwhen present on the solid particles introduced into the subterraneanformation. A particularly preferred product is a condensation reactionproduct comprised of commercially available polyacids and a polyamine.Such commercial products include compounds such as mixtures of C₃₆dibasic acids containing some trimer and higher oligomers and also smallamounts of monomer acids which are reacted with polyamines. Otherpolyacids include trimer acids, synthetic acids produced from fattyacids, maleic anhydride, acrylic acid and the like. Such acid compoundsare available from companies such as Witco, Union Camp, Chemtall andEmery Industries. The reaction products are available from, for example,Champion Chemicals, Inc.

[0021] The polyamides can be converted to quaternary compounds byreaction with methylene chloride, dimethyl sulfate, benzylchloride,diethyl sulfate and the like. Typically, the quaternization reaction canbe effected at a temperature of from about 100° F. to about 200° F. overa time period of from about 4 to 6 hours.

[0022] The quaternization reaction can be employed to improve thechemical compatibility of the tackifying compound with the otherchemicals utilized in the treatment fluids. Quaternization of thetackifying compound can reduce effects upon breakers in the carrierfluid and reduce or minimize the buffer effects of the compounds whenpresent in carrier fluids.

[0023] Additional compounds which can be utilized as tackifyingcompounds include liquids and solutions of, for example, polyester,polyethers and polycarbamates, polycarbonates, styrene/butadienelattices, natural or synthetic resins such as shellac and the like.

[0024] The non-hardening tackifying compound used can be coated on drysolid particles and then the coated solid particles mixed with thecarrier fluid or the tackifying compound can be mixed with the carrierfluid containing suspended solid particles and coated thereon. In eitherprocedure, the tackifying compound is coated on the solid particles inan amount of from about 0.01% to about 5% by weight of the solidparticles. More preferably, the non-hardening tackifying compound iscoated on the solid particles in an amount in the range of from about0.5% to about 2% by weight of the solid particles.

[0025] The particulate or other shaped solid material of larger sizethan the solid particles that is mixed with the tackifying compoundcoated solid particles suspended in the carrier fluid can include, butis not limited to, fibers, shavings, platelets, deformable particles andirregular shaped pieces. Of these, deformable particles are generallypreferred. The fibers, shavings, platelets, deformable particles andirregular shaped pieces can be formed of various solid materialsincluding, but not limited to, glass, ceramic, rubber, silicon, plastic,polymer, resin and metal. The deformable particles are preferably formedof rubber coated proppant, resin beads, soft metal particulates, resincoated metal particulates and the like.

[0026] When the larger solid material is mixed with the tackifyingcompound coated solid particles suspended in the carrier fluid, thetackifying compound coated solid particles stick to the larger solidmaterial and as a result, the larger solid material is uniformlysuspended in the carrier fluid along with the solid particles. Asmentioned, without the tackifying compound coating on the solidparticles suspended in the carrier fluid, the larger solid materialeither floats to the top of the carrier fluid or settles to the bottomof the carrier fluid depending upon the physical property differencesbetween the solid particles and the larger solid material such as size,shape, specific gravity, etc.

[0027] The larger solid material is mixed with the tackifying compoundcoated solid particles in an amount in the range of from about 0.1% toabout 100% by weight of the tackifying compound coated solid particles.

[0028] Another method of the present invention for treating asubterranean formation is comprised of the following steps. A viscousfracturing fluid containing suspended proppant particles which have beencoated with a non-hardening tackifying compound is introduced intofractures formed in the subterranean formation. Deformable particles oflarger size than the proppant particles are mixed with the fracturingfluid and the tackifying compound coated proppant particles suspendedtherein whereby the proppant particles stick to the deformable particlesand the deformable particles are uniformly suspended in the fracturingfluid along with the proppant particles. The deformable particles andthe tackifying compound coated proppant particles stuck thereto aredeposited in the fractures in the subterranean formation so that uponflowing back fluid from the formation the proppant particles and thedeformable particles do not flow-back.

[0029] The viscous fracturing fluid and the non-hardening tackifyingcompound are the same as those described above as are the proppantparticles and the larger deformable particles.

[0030] A preferred method of this invention for treating a subterraneanformation is comprised of the steps of: (a) introducing a carrier fluidcontaining suspended solid particles which have been coated with anon-hardening tackifying agent into the subterranean formation; (b)mixing a particulate or other shaped solid material of larger size thanthe solid particles with the carrier fluid and the tackifying compoundcoated solid particles suspended therein whereby the smaller solidparticles stick to the larger solid material and the larger solidmaterial is uniformly suspended in the carrier fluid along with thesmaller solid particles; and (c) depositing the larger solid materialand the tackifying compound coated smaller solid particles stuck theretoin the subterranean formation so that upon flowing back fluid from theformation the smaller solid particles and the larger solid material donot flow-back.

[0031] Another preferred method of the present invention for treating asubterranean formation is comprised of the steps of: (a) introducing aviscous fracturing fluid containing suspended proppant particles whichhave been coated with a non-hardening tackifying compound into fracturesformed in the subterranean formation; (b) mixing deformable particles oflarger size than the proppant particles with the fracturing fluid andthe tackifying compound coated proppant particles suspended thereinwhereby the smaller proppant particles stick to the larger deformableparticles and the larger deformable particles are uniformly suspended inthe fracturing fluid along with the smaller proppant particles; and (c)depositing the larger deformable particles and the tackifying compoundcoated smaller proppant particles stuck thereto in the fractures in thesubterranean formation so that upon flowing back fluid from theformation the smaller proppant particles and the larger deformedparticles do not flow-back.

[0032] In order to further illustrate the methods of this invention, thefollowing examples are given.

EXAMPLE 1

[0033] Without Tackifying Compound—250 grams of 20/40-mesh bauxiteproppant was mixed in 300 cc of 30-lb-per-1000 galloncarboxymethylhydroxypropyl guar fracturing fluid.

[0034] While stirring using an overhead stirrer, 65 grams of deformable,rubber-coated particulate was added to the proppant slurry. Afterstirring was stopped, the content was allowed to settle. An obvioussegregation of particles was observed as most of the deformableparticulate settled on top of the proppant pack.

EXAMPLE 2

[0035] With Tackifying Compound—250 grams of 20/40-mesh bauxite proppantwas first coated with 2.5 cc of tackifying compound known by the tradedesignation “SANDWEDGE-NT™ (Halliburton Energy Services, Inc.) bystirring with an overhead stirrer. The treated proppant was then mixedwith 300 cc of 30-lb-per-1000 gallon carboxymethylhydroxypropyl guarfracturing fluid. While stirring using an overhead stirrer, 65 grams ofdeformable, rubber-coated particulate was added to the proppant slurry.After stirring was stopped, the content was allowed to settle. Incontrast to what was observed in Example 1, there was no segregation ofparticles among the proppant slurry. The deformable particulatedistributed evenly in the proppant pack.

[0036] Thus, the present invention is well adapted to attain the objectsand advantages mentioned as well as those which are inherent therein.While numerous changes may be made by those skilled in the art, suchchanges are encompassed within the spirit of this invention as definedby the appended claims.

What is claimed is:
 1. A method of producing a fluid for use in treating a subterranean formation comprising providing a carrier fluid containing suspended solid particles which have been coated with a non-hardening tackifying agent and mixing with said coated particulate a deformable particulate of larger size whereby said smaller solid particles stick to said larger deformable particulate and said larger deformable particulate is suspended within said carrier fluid.
 2. The method of claim 1 wherein said carrier fluid is comprised of an aqueous gelled fluid.
 3. The method of claim 1 wherein said non-hardening tackifying compound comprises at least one member selected from the group consisting of polyamides, polyesters, polyethers, polycarbamates, polycarbonates, styrene-butadiene lattices and natural and synthetic resins.
 4. The method of claim 1 wherein said non-hardening tackifying compound is comprised of a polyamide.
 5. The method of claim 1 wherein said suspended solid particles comprise at least one member selected from the group consisting of graded sand, walnut hulls, bauxite, ceramic materials, glass materials and polymer beads.
 6. The method of claim 1 wherein said suspended solid particles are comprised of graded sand.
 7. The method of claim 1 wherein said non-hardening tackifying compound is comprised of a polyamide which is the condensation reaction product of a dimmer acid containing some trimer and higher oligomers and some monomer acids with a polyamine.
 8. The method of claim 7 wherein said polyamide tackifying compound is coated on said solid particles in an amount in the rage of from about 0.01% to about 5% by weight of said proppant particles.
 9. A composition comprising a fluid containing suspended deformable particles having smaller solid particles having a non-hardening tackifying agent coated thereon adhered thereto.
 10. The composition of claim 9 wherein said non-hardening tackifying agent comprises at least one member selected from the group consisting of polyamides, polyesters, polyethers, polycarbamates, polycarbonates, styrene-butadiene lattices and natural and synthetic resins.
 11. The composition of claim 9 wherein said non-hardening tackifying agent is comprised of a polyamide.
 12. The composition of claim 9 wherein said suspended solid particles comprise at least one member selected from the group consisting of graded sand, walnut hulls, bauxite, ceramic materials, glass materials and polymer beads.
 13. The composition of claim 9 wherein said fluid comprises an aqueous fluid and a gelling agent comprising at least one member selected from natural and derivatized polysaccharides which is capable of increasing the viscosity of the aqueous fluid.
 14. The composition of claim 13 wherein the gelling agent is crosslinked to further enhance the development of viscosity in the composition.
 15. The composition of claim 9 wherein said non-hardening tackifying agent is comprised of a polyamide which is the condensation reaction product of a dimmer acid containing some trimer and higher oligomers and some monomer acids with a polyamine.
 16. The composition of claim 9 wherein said polyamide tackifying compound is coated on said smaller solid particles in an amount in the rage of from about 0.01% to about 5% by weight of said smaller solid particles. 